1. Field of the Invention
The present invention relates to a discharge ability estimating system for estimating a discharge ability of a battery for supplying electric power to an electric motor which rotates a crankshaft of an engine to start the engine, an idling system incorporating the discharge ability estimating system, an electric device starting system including the discharge ability estimating system, and a discharge ability estimating method.
2. Description of the Related Art
Some vehicles including engines, such as a motorcycle, employ a technique for stopping idling during a stopped state. In this technique, when the vehicle stops driving, running of the engine is stopped, and thereafter a starter motor is actuated automatically to start the engine when the vehicle resumes driving. In this technique, since the starter motor starts the engine repeatedly, an electric power consumption amount of the battery is greater in this vehicle than a vehicle which continues to be idle during a stopped state. Therefore, it is more likely that electric power charged in the battery runs out, and as a result, the engine cannot be started. To avoid this, it is desirable to estimate a discharge ability of the battery. The discharge ability of the battery can be estimated based on an internal resistance of the battery, a maximum discharge current amount of the battery, and a voltage of the battery at a current (present) time. As a method of deriving the maximum discharge current amount, there is a method of detecting the maximum discharge current amount by a sensor, and a method of estimating the maximum discharge current amount like an in-vehicle battery state estimating system disclosed in Japanese Patent NO. 4459997.
To detect the maximum discharge current amount of the battery by using a sensor, the sensor is required to measure the maximum discharge current amount with higher accuracy. Such a highly accurate sensor is very expensive, and is undesirable in terms of cost saving. As a solution to this, Japanese Patent No. 4459997 discloses that the maximum discharge current amount of the battery is estimated based on the internal resistance of the battery. However, polarization may occur after the battery stops discharging, and this causes the calculated internal resistance to be lower than an original internal resistance of the battery. The polarization tends to be diminished with a passage of time after the battery stops discharging. Therefore, it is difficult to accurately know influence of the polarization.